The invention relates to a process for the utilization of slag coming from the ironworks industry and containing oxidic iron particles with a reducing agent being added and with oxidic iron particles of the slag as well as other metal oxides which optionally are provided being reduced by means of said reducing agent, as well as to an installation for carrying out the process.
Processes for the beneficiation of slags from the ironworks industry are aimed at forming environmentally compatible slags, which in particular are economically usable and, for instance, can be used as raw materials for the production of cement clinker substitute.
Processes of this kind are known, for example, from WO 96/24696 or from WO 97/46717. Thereby, iron-oxide containing liquid slags such as steelworks slag are mixed with iron-oxide carriers such as iron ores, basic weak ores, rolling mill scale or metallurgical dusts and lime and the ferrite slag thus formed is reduced in a reduction reactor whereby an iron bath and a sintering phase are formed with carbon being burnt, or hot air is injected, respectively.
A disadvantage of these known processes is the high amount of waste gas and the high dust loss resulting from the injection of residual materials and coal from below through the bath. Another disadvantage consists in that the heat loss caused by the endothermic reduction process during the reduction of the iron-oxide particles of the slag is compensated for chemically or by hot air, i.e. chemically by the combustion of carbon. These measures cause high turbulences and hence also high carbon losses due to the higher dust content and the larger amount of waste gas. The chemical heating caused by the combustion of carbon affects the chemical equilibria and hence the course of the process during the treatment of the slag. The high CO2 emissions inevitably arising thereby constitute an economic disadvantage in view of the CO2 taxes which will soon be payable and are not consistent with the trend toward sustainable processes. Furthermore, the utilization of slag takes place in converters or stationary reduction reactors of a complex design, necessitating high investment costs.
Another disadvantage of the known processes is that the operation is discontinuous, i.e. slag to be treated is charged, finished and after that is cast or tapped, respectively. This involves vigorous reactions for each slag batch, accompanied by a substantial change in the chemical compositions of the phases present in the reactor vessel, which in turn causes a high strain on the fireproof lining of the reaction vessels, i.e. of the converters or stationary reduction reactors. This high strain is additionally intensified by the above-mentioned chemical heating.